This invention relates to an apparatus for hydrating and extracting residual materials from a lens, especially a contact lens, and methods employing the apparatus.
Soft, hydrogel contact lenses are produced by polymerizing a monomeric mixture comprising a hydrophilic monomer and a crosslinking agent. The monomeric mixture can be cast directly into lenses by static cast molding or spincasting methods, where the liquid monomeric mixture is charged to the mold and is then cured, typically by subjecting the monomeric mixture to UV radiation, heat or both. Alternately, the monomeric mixture can first be cured in the form of cylindrical blanks (also referred to in the art as "buttons"), which buttons are then lathe cut into lenses, or buttons can be cut from rods or sheet of cured lens material for lathe cutting into lenses.
Regardless of the manner of forming the lens, following polymerization (or curing) of the monomeric mixture such soft lenses are typically hydrated by exposure to water or an aqueous solution under appropriate conditions that the lens-shaped article absorbs and retains water to form a hydrogel. Also, the lenses are typically treated to extract undesired residual materials remaining in the lens from the polymerization process. Such extractibles may include incompletely polymerized monomers, oligomers formed from the curing process, and any diluent or solvent present in the initial monomeric mixture. The extraction may be performed as a process step separate from the hydration process, or these two processes may be performed simultaneously.
As an example, U.S. Pat. No. 5,271,875 discloses a method of static cast molding lenses in a mold assembly composed of anterior and posterior mold sections. The method includes introducing monomeric mixture to the mold assembly, curing the monomeric mixture to form a lens, and recovering the lens and hydrating the lens to form a soft hydrogel lens. U.S. Pat. No. 5,271,875 illustrates two general methods of recovering the lens from the mold and hydrating the lens. First, in a "wet release" process, the lens is hydrated while retained in a mold section, the hydration process also facilitating removal of the lens from the mold section in which it is retained. Second, in a "dry release" process, the lens is first disengaged from the mold section in which it is retained by a force applied by a mechanical fixture, whereby the lens is hydrated after removal from the mold. U.S. Pat. No. 5,264,161 also discloses a "wet release" method of recovering a lens, where a contact lens and the mold in which it is retained are added to an aqueous bath including a surfactant.